Nanoimprint lithography, also often called imprint lithography, is capable of replicating patterns on a pre-made mold as small as several nanometers. The pre-made mold has extruded areas and recessed areas on its replication surface, which constitute patterns of various shapes and sizes. The mold was typically made by a patterning step using electron beam lithography (EBL) or mixing of EBL and optical lithography, and, a follow-up etching step using reactive ion etching (RIE) to create the patterns. Nanoimprint lithography starts from applying a volume of polymer onto a substrate by either spinning or dispensing. The polymer is either flowable in ambient temperature, or, from rigid to deformable or flowable by thermally heating. Then, the pre-made mold is positioned to contact with the substrate. After that, the mold is pressed against the substrate. If the polymer is in liquid in ambient temperature, pressing the mold against the substrate will force the surface extrusion areas on the mold replication surface to go into the layer of the polymer. If the polymer is rigid in ambient temperature, a thermally heating step is conducted prior to the contact, after the contact but before the pressing, or during the pressing to make the polymer deformable or flowable. Thus, pressing the mold against the mold is able to force the surface extrusion areas on the mold replication surface to go into the layer of the polymer. When the extruded areas completely go into the layer of the polymer, the polymer is transited from deformable or flowable into rigid by UV radiation, thermally heating or thermally cooling depending on types of the polymer. At last, the mold is released from the substrate while the layer of the polymer attaches to the substrate. To prevent the polymer from sticking to the mold, a very thin release coating can be deposited on the replication surface of the mold. Typical release coating included surface release surfactant and per-fluoro polymer deposited by CVD. After the substrate is separated from the mold, the extrusion areas on the mold surface are corresponding to the recessed areas in the polymer layer. Therefore, a reverse-tone replication of the patterns on the mold is formed onto the polymer film on the substrate. The polymer can be a thermo-plastic polymer or curable polymer. A thermo-plastic polymer transits from rigid to deformable or flowable when being heated above its glass transition temperature, and, vice versus when is cooled below its glass transition temperature. A curable polymer is deformable or flowable originally, and transit to rigid when being heating to curing temperature for thermo-set type or being cured under UV exposure for UV-curable type. When alignment is needed, the mold is aligned with the substrate through a set of matching align markers prior to the contact. Previously, electron beam lithography is very slow to write nanoscale patterns. It is unlikely to use it for mass production of nanoscale devices. Nanoimprint lithography is able to replicate whole area of patterned surface of the pre-made mold onto the substrate by one cycle of the process. It can dramatically increase the efficiency of patterning nanoscale features. Because the mold is repeatedly used for many cycles of imprinting, the high cost of using electron beam lithography to make the mold is averaged into these many imprints. Nanoimprint lithography delivers a practical method to produce nanoscale devices at low cost.
Since its invention in 1995 by Stephen Y. Chou (referring to U.S. Pat. No. 5,772,905), nanoimprint lithography has successfully demonstrated its capability of replicating a feature as small as 5 nm. Meanwhile, many research works were carried out on developing resists for imprinting, mold making techniques, mold release coating for clean separation, and apparatus to do imprinting. In overall, nanoimprint lithography has evolved into being a widely used technology for research laboratories, but not reached a stage ready to meet much higher requirements of industrial use. One of the critical improvements needed by industrial use is imprint system and method with high throughput and overlay accuracy.
Fast nanoimprint apparatus is highly demanded by semiconductor, opto-electronics, and magnetic media industries to use this technology to manufacture nano-scale device products. Prior to the invention, the apparatus of nanoimprint lithography conducted aligning and contacting the mold with the substrate and pressing the mold against the substrate on two different sites within frame of the apparatus. Separating the mold from the substrate was often conducted on either one site of them or a third site. This basic design approach demanded to transfer the contacted mold/substrate set among these sites to finish a full cycle of operation. Thus, throughput of the apparatus, which is defined as time consumption to finish a cycle of imprinting, is severely degraded by time cost of transferring among these different sites. Furthermore, the internal transferring increases mechanical complexity of the apparatus and potentially introduces mechanical failure during operation. An apparatus capable of completing a full cycle of imprinting process on one site within its frame limit will potentially achieve much higher throughput and reliability.